Dewaxing mineral oil



Patented Oct. 6, 1953 DEWAXING MINERAL 01L Charles F. Sacra, Alton, Ill., assignor to Shell Development Company, corporation of Delaware Emeryville, Calif., a

N Drawing. Application February 27, 1951, Serial No. 213,060

2 Claims. 1

This invention relates to a process for the separation of petroleum into solid and liquid fractions. The process of the invention is particularly adaptable to the separation of crystalline and amorphous waxes from lubricating oil distillates and petroleum residues. It may be utilized in the treatment of any petroleum fraction from which it is desired to separate waxy material.

Many crude oils from which lubricating oil is produced contain wax. Wax is found associated with the lubricating oil fractions of parafiinic base crude oil and with the lubricating oil fractions produced from many of the so-called mixed base and asphaltic base crude oils. It is not only of doubtful lubricating value but limits the temperature at which lubricants containing it may be used. At low temperatures a wax-containing lubricating oil congeals to a semi-solid state. The temperature at which an oil congeals is commonly referred to as its pour-point. Therefore in the production of lubricating oil from petroleum fractions containing wax it is advantageous and customary to remove a substantial portion of the wax or wax-like substances present in the oil in order to lower the pour-point of the oil so that the lubricating oil may be effectively used at low temperatures.

Several methods well known in the art are employed at present for the production of low pour-point lubricating oil stock from petroleum fractions which contain wax. Briefly described these methods employ a liquid which is a solvent for all the liquid components of oil at the dewaxing temperature but which has almost no solubility for all the solid components thereof at the same temperature. The dewaxing temperature employed depends upon the desired pour-point of the lubricating oil or upon the amount of wax to be removed. For example, in conventional dewaxing processes, such as propane dewaxing or solvent dewaxing employing a mixture of methyl ethyl ketone, benzene and toluene, if it is desired to produce a lubricating oil having a pour-point of about l0 FL, it is necessary to carry out the dewaxing operation at a temperature of about -45" F. to about 50 F. in a propane dewaxing process and at a temperature of about -25 F. in the above-mentioned solvent dewaxing process. If it is desired to produce a lubricating oil having a pour-point of about 0 F., the dewaxing temperature must usually be about 35 F. and about F. for a propane dewaxing and a solvent dewaxing process respectively. Thus, the pour-point of a petroleum lubricating oil depends to a great extent upon the dewaxing temperature employed. As indicated, the temperature differential between the dewaxing temperature and the pourpoint of the dewaxed oil in conventional commercial propane dewaxing operation is considerable, usually at least 30 F. While the temperature differential between the dewaxing temperature and the pour-point of the dewaxed oil in the conventional solvent dewaxing with MEK, benzene, and toluene is usually only 10 to 15 F., this solvent mixture requires external refrigeration which entails additional equipment, materials and expense.

It is an object of this invention to provide a method for obtaining a lubricating oil which has a pour-point substantially the same as the dewaxing temperature and to provide a method for obtaining a lubricating oil which has a pour-point appreciably lower than that obtained by conventional propane dewaxing and at least comparable to that obtained by methyl ethyl ketone, benzene and toluene solvent dewaxing at the same dewaxing temperature. It is another object of this invention to provide a method for dewaxing lubricating oil to yield lubricating oils of low pour-point at a relatively high dewaxing temperature and which permits rapid filtration and washing rates of the resulting wax cake. It is still another object of this invention to provide an economical method of producing a lubricating oil having a low pour-point. These and other objects of the invention will become apparent from the discussion of the invention as set forth hereinafter.

It has nowbeen discovered that lubricating oil possessing a low pour-point, substantially the same as the dewaxing temperature employed, may be produced by a method which comprises dewaxing a wax-containing mineral oil fraction. such as a lubricating oil distillate or petroleum residue, with a liquid solvent mixture of a normally gaseous, readily liquefiable hydrocarbon, such as propane, or a liquid mixture of hydro carbons containing the same, and an alkanone and/or an alkenone and/or an alkanol of 4 to 5 carbon atoms inclusive, and particularly methyl ethyl ketone and/or methyl isobutyl ketone. More particularly it has been discovered that raw (wax-containing) petroleum distillates and raw (wax containing) petroleum residues, deasphalted if required, may be processed (dewaxed) 3 to produce a lubricating oil having the desired pour-point by a treatment which comprises: dissolving the wax-containing mineral oil fraction in a liquid solvent such as methyl ethyl ketone, mesityl oxide, and methyl isobutyl ketone, or a mixture thereof, at a suitable elevated temperature, usually within the range 100 F.-200 F., depending upon the volume ratio of the liquid solvent tothehydrocarbon material to be dewaxed; cooling the resulting solvent-oil- -solutionto .a selected dewaxing temperature and at the same time introducing into said solution an amount of liquid propane so that, at said selected dewaxing temperature, the proportion of litiuidsnlvent' to liquid propane is between about 1 :9 by volume and about 4:1 by volume, cooilmg being effected either by means of an external relrigerant or preferably by employing propane as an internal refrigerant.

For obvious reasons it is preferred that propane I be employed as an internal refrigerant.

may conveniently and. readily be accomplished (as is well known by those skilled in the art) by adjusting the feed rate and amountcfthel'iquid propane to the solvent-oil solution and at the same time adjusting the rate and: amount of gaseous propane vaporizing therefrom. During the cooling step, agitation of the resulting admixture may advantageously be employed. As required or desired, vaporization of the liquid propane may be carried out atsubatmospheric or at atmospheric pressures. It is' also possible to vaporize the liquid propane at a pressure greater than atmospheric, being limited of-course' by the vapor pressure of propane" at theparticular temperature.

With reference to the specialsolvent mixture of the invention, in accordance with a preferred embodiment thereof, itis preferred to employ a liquid solvent mixture of propane and methyl ethyl 'ketone when dewaxing a wax-containing petroleum distillate fraction. The use of'a liquid solvent mixture of propane andmethyl 'isobutyl ketone when dewaxing'a wax conta'iningpetroleum residue represents anotherpreferred practice; In

general the invention is particularly applicable to the dewaxingiof a high viscosityindexwaxy'oil, i. e., a petroleum fraction which doesnnt contain an appreciable amount of monocy'clic. aromatic compounds. The invention, however, is applicable to both solvent extracted and unex tracted oils. When the invention is applied to residual petroleum stocks, suchas a waxy short residue, these stocks should advantageously be first deasphalted if necessary.

As indicated hereinbefore, in a conventional propane dewaxing process where'inliquid propane is employed both as an internal refrigerant and as. the. only solvent, the pour-point of the .dewaxed oils is usually about -45 F; higher than the dewaxing (wax-filtering) temperatu-rei Similarly in a dewaxing process...employing the con,- ventional solvent mixture ofmethylethylLketone, benzene and toluene the pour-point-of theresulting dewaxed oil. is about. 10-15 F.. higher than the dewaxing temperature. Propane. d'ewaxing however'has .an advantage in that. propane may also be employed as an internal. refrigerant whereas in .a methyl ethyl ketone (hereinafter referredto as MEK) -benzene-toluene solvent dewaxing operation an-external refrigerant-must. be employed. This isa-disadvantage sinceradditional equipment must be employed andthe dewaxing operation is more expensive.

A dewaxingprocess. employing: asolventimixture consisting of MEK, benzene and toluene and wherein propane is utilized as an internal refrigerant, does not aiford a satisfactory method of producing low pour-point lubricating oils. The pour-point of a dewaxed lubricating oil produced by such solvent treatment is usually about 20-25 F. higher than the dewaxing temperature employed. For example, when employing a solvent mixture of MEK-benzene-tolnene in the proportions by vo1ume-,40-40+2'0, respectively; at dewaxing temperatures of -15F. and -3'0F. the dewaxed lubricating oils produced had a pour-point 20 and 25 13. higher, respectively, than the dewax'mg'temperature. These great differences between pour-point and dewaxing temperature were due-to the iact'tl'rat' propane comprised approximately 10-20% bywolume of the solvent mixture present in the filtrate. The resulting excessive solventiaction ofQ-the propane in addition to the M-EK-benzene-toluene retarded wax precipitation (increased its solubliity in the solvent-oil solution) and as a result gave pour-points 20-25 F. higher than the dewaxing temperature. Furthermore,.it was not possible-to remove-all of thepropane even when the dewaxi'ng and propane removal (propane being used as an internal refrigerant) were carried out at relatively low pressures, in the order of 3-20-inches mercury absolute. Additionally it was found that lower dewaxing temperatures favored an increase in the amount of propane retained in the solvent-oil solution.

Oxygen-containing polar organic compounds such as methyl ethyl ketone (MEK), mesi'tyl oxide (hereinafter referred-to as MO) and methyl isobutyl ketone (hereinafter referred to as MIBK) reduce the solubility ofwax-materials in mineral oil. These solvents however are also poor solvents' for the liquid (non-wax) components of mineral oiL This is not surprising; in view of the markedly similar chemical and physical properties of the. normally solid (wax) and liquid (oil) components of mineral.oiL The dewaxing solvent of the invention may 'if' desired be modified "by other solvents, especially'the well known dewaxing solvents- Aromatic hydrocarbons such as benzene, toluene should not be included and. are undesirable because. of the relatively large solubility of waxes therein.

It is possible however by employing'a'polarmaterial. suchas MEK', MO and MIBK or mixture of the same as a dewaxing solvent, to produce a lubricating oil having a pour-point identicalto or substantially the same. as, i'. e., not. greaterthan 10 above, the dewaxing temperatura Be.- cause of the poor solubility of petroleumfractions in these polar solvents a high solvent. to oil ratio must be-employed, at least 1.0, vusually'30 volumes of. the polar solvent, (MEK, MO orIMLBK) per volume of hydrocarbon material. to be dewaxed. However, .sincethe. polar solvent in. a. commercial operation. must berecovered and. recycled, this methodis not. economically practical; because of the. excessive costofthe solventrecovery opera tions.v Furthermore, at. .low temperatures and particularly at low solvent to hydrocarbonratios, demixing usually occuraresultinginthe..formaition of. three. phases, a solid phase wax, a liquid polar solvent phase. and a hydrocarbon phase. which contains. a considerableamount. of the undesiredwax.

Solvent mixtures comprising, a polar organic liquid, particularly MEK,.MO or. MIBKormixtures: of the same, and propane, whereimpropane isemployednotronly activesolventibutalso as an internal refrigerant are however excellent dewaxing solvents. Particularly effective solvent compositions comprise a liquid mixture of a polar solvent and propane wherein the volume ratio of the polar organic liquid to propane is between about 1:1 and about 4:1. An especially effective solvent composition comprises a liquid mixture of a polar solvent, such as MEK, MO and MIBK, and propane wherein the volume ratio of the polar solvent to the propane is about 7:3.

In the dewaxing operation according to the process of the invention, various ratios of solvent to the wax-containing mineral oil material may be employed, depending upon the desired pour-point of the lubricating oil to be recovered,

the degree of dewaxing sought, the amount of waxy material present in the raw mineral oil fraction (distillate or residue) and upon the equipment available as well as sundry economic and practical considerations. vent to mineral oil volume ratio of from about 2:1 to about 10:1 is satisfactory, however, a volume ratio of from about 4:1 to about 6:1 is more preferred.

Advantages to be obtained by employing the process of the invention in a dewaxing operation, are illustrated by the results of a number of experiments which were carried out (1) wherein conventional dewaxing liquid mixtures of MEK- benzene-toluene were utilized as the dewaxing 3o solvent, employing propane as an internal refrigerant, and (2) wherein a liquid mixture of MEK- propane was employed as the dewaxing solvent, and at the same time employing propane as an internal refrigerant. The experiments were carried out in the following manner.

Dewaxing equipment normally employed for standard I-IVI crude evaluations was used for the dewaxing operations. The equipment consisted of a 7 /2 gallon pressure vessel (bomb) and a separate externally chilled filter with a 0.66 sq. ft. filter area. A hot water bath was used for preliminary heating of the pressure vessel and its contents to the desired solution temperature.

An insulating jacket was provided to enclose the vessel during the chilling and filtering periods.

The wax-containing lubricating oil distillate (wax content about 7.5% by weight and which after conventional furfural or phenol solvent extraction and dewaxing yields a raffinate having a viscosity of 250 S. S. U. at 100 F.), conse- In general a sol- 2o quently termed a 250 distillate, from a West Texas Ellenburger (WTE) base stock and dewaxing solvent were charged to the dewaxing bomb. In the case of MEK-propane dewaxing the MEK was added at this point and the propane was added later, as described hereinafter. In a similar manner the solvent mixtures of MEK-benzene and toluene were added. The bomb was then immersed in the heating bath and heated to about 140 F. to assure complete solution of the oil and wax in the solvent. The bomb was then removed from the heating bath and the contents thoroughly mixed by end over end rotation of the bomb. After enclosing the bomb in the insulating Jacket in a vertical position on a suitable platform scale, flexible hoses to propane feed and suction lines were connected and suitable valves opened to start the chilling cycle. The propane feed and suction line valves were regulated to maintain suitable chilling rate. Inthe case of the MEK-propane dewaxing experiments the amount of propane is additionally controlled in order to achieve the desired MEK- propane volume ratio at the dewaxing temperature.

When the desired dewaxing temperature was reached, suction was applied until a constant weight (in the case of the MEK-benzene-toluene solvent dewaxing) or a desired weight was reached (usually in the case of the MEK-propane solvent dewaxing). The propane lines were then disconnected and the pressure vessel connected to the chilled filter. An air line provided with a pressure gauge and a pressure regulating valve was attached to the inlet at the top of the bomb and the vent on the filter opened until the filter was full of liquid. After adjusting the pressure regulator to 10 p. s. i. g. and opening the discharge port of the filter, the filtration was timed to the point of pressure drop on the gauge. The solvent was then stripped from the dewaxed oil and wax and the resulting products weighed.

When external chilling was used instead of internal (propane) chilling, the same procedure of heating and mixing the bomb was used but the bomb was chilled in a kerosene bath refrigerated with Dry Ice, prior to attachment to the chilled filter.

The results of these experiments are set forth in Tables I and II.

TABLE I MEK Dewaxmg of WTE 250 Dzstzllate Run A B C D E F G H J Solvent Oil Ratio, by vol 2 1 3 4 4 1 4 4 4 l 4 I 4 Solvent Composition:

MEK, percent v 40 40 40 40 40 40 40 40 Benzene, percent v. 40 40 40 30 40 40 40 40 40 Toluene, percent v. 20 20 20 10 20 20 20 20 20 Dewaxing Temp., F 5 l5 15 15 15 30 30 --l5 --3() Yield, Oil Recovery:

Percent w 3 79. 0 83. 4 82. 4 81. 2 83. 8 77. 7 80. 0 73. 0 Percent v 5 79- 0 83. 4 82. 3 81. 1 83. 8 77. 6 69. 7 72. 8 Propane in Filtrate, percent 14. 2 ll. 8 24. 2 16. 9 4. 8 l7. 2 er Rate, G. P. H./Sq. Ft. 6 3 6 7 3 4 6 3 Oil Properties:

PI G 26. 4 26. 5 26 2 26. 2 26 4 26 2 25. 8 26. 1 284 308 273 297 301 308 299 312 51 53 51 52 53 52 53 96 94 95 95 04 94 94 395 440 380 400 440 455 450 Pour-Point 5 5 0 5 0 5 -5 5 3 -12 (PPDWT) 20 15 20 15 10 25 25 18 18 1 Propane after chilling contained 0.10% v. MEK, 0.22% v. benzene and 0.03% v. toluene. 2 External chilling with no agitation.

I Vacuum increased to 26 inches mercury during chilling.

4 G. P. H./sq. ft.=gallons per hour per square foot of filter area.

I Average of three determinations.

Pour-point minus the dewaxing temperature, T.

LEZII fPropane MEK TDe-wamizry of WTE Z50 .Distiltate 'VDesignatlons-are thesame'as ln'Table'I.

The-data of Table'I demonstrate that a dewaxing operation, "employinga solvent mixture "of .;MEKbenzene=-toluene :and advantageously utilizing propane .as an internal refrigerana'consistently yields a dewaxed-lubricating oil *having a pour-point considerablyhigher than the dewaiiingiemperaturaat least 15 F. up to 25 F. higher. Furthermore the wax-filtration #rates are low, consequently restricting production of "botlrwax and dewaxed lubricatingoil.

"Thedata set'forth in Table II, however, illustrate that-whena liquid'MEK-propane dewaxing "solvent is employedthe pour-point of the result- -irrg dewaxed oil approaches the 'dewaxing temperature. 'For example when MEKand' propane are employed in a volume ratio between "about 1:1 and about 4:1 the pour-point of the de- 'w-axed'llubricating .oil is not greater than 8 -F. above the -devvaxing temperature and ataMEK .zto propane volume ratio p'f T7 :3 1thetemperature differential between the pour-point of "the de- Waxed .oil .and. the dewaxing temperature amourrtsto only 2;F.

As indicated hereinbefore, the drumming temperature employed depends to .a. .great extent .upon the extent .of wax-=removaldesired. .Asa general rule to .obtain a relatively wax-'free'lubrieating oil or petroleum fraction (e. g., a very low'pour-p'oint lubricating oil) relatively low dewaxing temperatures are required. .In'the'practime of this invention it is preferred, however, to operate at a dewaxing temperature ofbetween about F. and about 40 theitemperature range between about l F. andabout 30 .F. being preferred.

, Another advantage of the invention, as illustrated by the data set forth in'Table II .is-that the'filtration rate of the wax-solvent-oil ad1if1x 'itnre-atithe-newaxing mperatureiiszereatly inczeased. ;Eor;example,iatrsolventrratios-sor:MEK the propane :of l: 1 :and :3 r2 rthetfilter :rates, TEX- :pressedzasrgallons penhnperzs zft. .of filtering :area,:ait :a temperature 10f -:15.;F., arel and :17, :respeotivly. Whereas, atsa. solvent :ratio 1315 lvlEK to'fpropan'erof '7:3-thezfilterrateiis:37, increasesiof I600 :and .'abouti120:% rrespectively.

:A'jeature of ;the invention is that :by the use of wax conditioners thexfiltration:ratezofthewaxi-solventeoil admixture .may be i'substantially "increased. .Added advantages :a'coruing atherefrom .-:are that the ryield pf is increased :by :the'ause 'of a Wax nonditioner, filtration rate :may be inrcreased;asnnuchzasrseverathundredmer 'centzand the "per :cent yield of :oilnnay :be increased A to 3%. rgeneral :those which are well known :in the art as pour=point depressants are :also :suitable aswvax conditioners :inthe practice cof the invention. "ifIhese wax .zconditionersu-may :rbe :addedjn anramountup rtotaboutl' by volumezoi thmmaterialrto the .dewaxed.

LI .c'laimyas zmyzinvention:

1. The process of dewaxing a mineralllubrimatting "T011 distillate :icontaining about 1.5% by weight ?Of' Wa.X"WhiCh comprises: :cooling a liquid admixture 20f said wax-containing mineral -oil *distillate andia dewaxingsolvent consisting essentially 10f a liquid mixture of methyl ethyl ketone and propane, the solvent to on volume ratio being about 4:1 and the 'ketone to propane volume ratio being about '7 :-3,=to precipitate solid 'wax'irom' the-oil, and separating the-precipitated wax.

.2. The process .ofzdewaringsa substantially .asphalt-free waxecontaining mineral lubricating Oil distillate whichrcomprises: "cooling -.a rliquid :a'dmixture oi saidrmineralpil distillate and'a dewaxing vsolventcconsisting essentially of methyl ethyl: ketoneiand propane,- the: solvent to 'oilvolume ratio 'being from about 1411' to 61.1 and the eketonettopropane volume ratio being :rrom about toazrl, .-.to .rprecipitate zsolid wax from theoil, and separating the-precipitated wax.

ZCHAREES :F. "SACRA.

References Cited .in :the :file .of this patent UNITED STATES PATENTS 

2. THE PROCESS OF DEWAXING A SUBSTANTIALLY ASPHALT-FREE WAX-CONTAINING MINERAL LUBRICATING OIL DISTILLATE WHICH COMPRISES: COOLING A LIQUID ADMIXTURE OF SAID MINERAL OIL DISTILLATE AND A DEWAXING SOLVENT CONSISTING ESSENTIALLY OF METHYL ETHYL KETONE AND PROPANE, THE SOLVENT TO OIL VOLUME RATIO BEING FROM ABOUT 4:1 TO 6:1 AND THE KETON TO PROPANE VOLUME RATIO BEING FROM ABOUT 3:2 TO 4:1, TO PRECIPATE SOLDI WAX FROM THE OIL, AND SEPARATING THE PRECIPITATED WAX. 